What organism is the common ancestor to plants?

Many Protists share traits with plants

  • Dinoflagellates - unicellular aquatic
    • some are photosynthetic
    • haploid dominate life cycle


  • Brown Algae - large multicellular aquatic
    • AoG life cycle
    • photosynthetic but use chlorophyll c


  • Diatoms - unicellular aquatic
    • all are photosynthetic
    • diploid dominated life cycle





Dinoflagellates
Brown Algae
Diatoms


Not ancestral to plants!


Secondary endosymbiosis
for chloroplasts

The big picture: Plants evolved from green algae


  • Cyanobacteria & protist made landfall ~1.2 bya
    • plants, fungi and animals ~500 mya
    • first forests 385 mya


  • Plants evolved from green algae
    • several key ‘shared derived traits’


  • Plants support all other life on land
    • oxygen to breath
    • food to eat
    • new habitats for animals

Green Algae (genus = Oedogonium)


  • Sister group to land plants
    • all are photosynthetic
    • marine and freshwater
    • single and multi-cellular
    • broad, thick filaments (not stems)
    • some have A.o.G
    • evolved around ~750mya


  • Reproductive features:
    • Oogonia = egg containing cell
    • Antheridium = sperm containing cell
    • these ‘houses’ for egg and sperm are protections from the environment

Molecular evidence points at charophytes as plant ancestors

Many shared gene families with plants, now that we have the chara genome

Charophytes (freshwater green algae)

  • Freshwater species


  • Transition from water to land starts with Charophytes
    • freshwater habitats may have dried
    • ancestral species partly lived out of water


  • More shared traits with land plants: know a few!
    • circular protein rings in plasma membrane
    • make cellulose fibers in cell wall
    • swimming sperm with similar structure
    • phragmoplast (growth hormone)
    • ROS genes to eliminate free oxygen radicals

Living on Land: The Wild Wild West

What are the pros and cons of living on land?

Land plants are a monophyletic group

Shared derived traits define land plant evolution

Multi-cellular, Dependent embryos (placental transfer)

Fancy botany word for plants = embryophytes

Waxy cuticle and stomata

Multi-cellular Gametangia

Fancy botany term for sperm and egg houses

Photosynthesis with unique pigments (chlorophyll A & B)

Unique cell walls




  • Cells walls made of cellulose
    • not unique to plants


  • Pectin to fortify cell walls
    • unique to plants


  • Produce cells walls in unique way
    • at end of mitosis

Alternation of generations

Can you draw me yet?

First plant group: non-vascular bryophytes (mosses)


  • Mosses, hornworts and liverworts
    • Fossils of bryophyte spores ~470mya


  • Non-vascular; ground hugging carpets
    • bodies to thin to support height growth


  • Have a rhizoid but not a root
    • anchors plant
    • does not uptake water


  • Resistant spores

Bryophytes have a gametophyte dominated life cycle

Early plants, like moss, have sperm that swim from antheridia to archegonia